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911st 911st is offline
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Join Date: Jan 2004
Location: Sacramento
Posts: 7,269
Sorry if the AFR plot is hard to see but it is an example of what I call "lean surge" that comes with CIS.

I belive this motor is reported to idle at almost 14/1 AFR and cruse at near 14.7/1, with acclereration the AFR goes to about 16/1 over the first apx 200rpm and it is not until 2500rpm that the AFR stabilizes back to 14/1.

Max TQ is closer to 13/1 AFR.

To a lesser degree this is what I saw on my C2Turbo when I used a Motec Wide Band monitor before my WUR mods.

I am a big believer in proper ignition settings but curring what I call the CIS 'lean surge' can also help throttle response and can give that extra kick that gets the turbo spinning quicker.

There are two ways to correct for this with CIS. One is to instantly lower Control Pressure with acceleration via the D-WUR's programing or a vac-sensing conversion to the WUR . It still takes a half a sec before the accl AFR's respond fully but they do respond well.

The other would be to trick the Lambda function. This would be more instant but would not reduce the restriction of the metering plate on the suction side of the turbo.

It would be interesting to put a vac gauge in the section between the metering assembly and turbo to see how significant said restriction is.


Old 04-27-2010, 05:01 PM
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